Eminent Entomologists stir the Bt cotton pot

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Two prominent entomologists have criticised three recent studies on the effects of genetically engineered crops on insects saying the studies are unrealistic and have distorted the public debate.

The article, "False reports and the ears of men," in the latest issue of Nature Biotechnology, is authored by Anthony M. Shelton, professor of entomology at Cornell's New York State College of Agriculture and Life Sciences, and Richard T. Roush of the University of Adelaide, Australia. They urge that the public should not be swayed "by laboratory reports that, when looked at with a critical eye, may not have any reality in the field or even in the laboratory."

The first of the three studies they comment on was led by John E. Losey, Cornell assistant professor of entomology. In the May 20 issue of Nature, Losey and his colleagues reported that pollen from commercial corn, genetically engineered to produce a bacterial toxin to protect it against European corn borers, kills monarch butterfly larvae in laboratory tests (Losey Study). While Shelton and Roush note that this result was expected under such laboratory test conditions, they question whether this test was realistic.

"If I went to a movie and bought a hundred pounds of salted popcorn, because I like salted popcorn, and then I ate those the salted popcorn all at once, I'd probably die. Eating that much salted popcorn simply is not a real-world situation, but if I died it may be reported that salted popcorn was lethal," Shelton said in an interview.

Shelton and Roush voice their surprise that a "previous and more relevant and realistic study has been largely overlooked." While the Cornell laboratory study showed high mortality among monarch larvae that ingested genetically engineered pollen, an Iowa State University study by Laura Hansen and John Obrycki showed low mortality even when Monarch larvae were fed milkweed that had the highest levels of Bt pollen that would be encountered in the field. Shelton and Roush note that it is unlikely that these high Bt pollen levels would be encountered by the insects in the field.

In the second study discussed in the article, researchers at Kansas State University reported in Science that they had discovered corn borer resistance to Bt toxins. Shelton and Roush question the methodology used in the study, "including that the authors did not demonstrate that resistance was actually to the same Bt toxin as in the plant or that the insects could survive on the Bt plant."

The third study, in another recent issue of Nature, is from the University of Arizona showing that the pink bollworm's resistance to Bt-cotton was recessive in inheritance, but the paper questioned whether resistant bollworms developed more slowly than susceptible bollworms. This could possibly knock out random mating and dilute the insect's resistance in the field. "We hope that the take-home message won't be converted to another premature claim that Bt crops are doomed," Shelton and Roush say in their commentary.

Crops are genetically engineered with Bt to control pests without the use of broad spectrum insecticides, which may cause environmental and human health problems. For example, the European corn borer is the most notorious pest that corn farmers face and causes an estimated $1.2 billion in crop losses annually. To combat this pest, an estimated 24 to 28 million acres of Bt-corn were planted in the United States in 1999.